Accelerating the Thermal Response of a III-V/Si3N4 Hybrid External Cavity Laser With Electronic-Photonic Co-Design

We propose an electronic-photonic (EP) co-designed scheme to enhance the modulation speed of thermo-optic (TO) phase shifters. We establish a small signal analysis model to optimize the TO phase shifter by compensating its thermal-response-limited low-pass behavior with an electric high-pass equalization circuit, thus expanding the modulation bandwidth. To prove its potential, we demonstrate an EP-converged frequency-modulated continuous-wave (FMCW) laser comprising an InP/Si₃N₄ hybrid integrated external cavity laser (ECL) driving with an electric equalization circuit. The small signal bandwidth of the TO phase shifter inside the laser cavity is enhanced from 10 kHz to 360 kHz with the equalization circuit. By driving the TO phase shifter, we generate an FMCW signal with a chirp bandwidth of 943 MHz at a repetition rate of 100 kHz. The residual nonlinearity of the frequency chirp is reduced to 0.72% thanks to the pre-distortion technique, enabling a ranging precision of 8.1 cm over a 20 m distance.